Conventional transmitters and receivers employ a plurality of serially connected digital and/or analog components to propagate or receive, respectively, an electromagnetic signal. As illustrated in FIGS. 1A and 1B, respectively, conventional transmitter chain 100 and conventional receiver chain 200 each comprise a plurality of digital and analog components (e.g., a low-noise amplifier [LNA], a variable-gain amplifier [VGA], a base-band amplifier [BBA], a multiplier or mixer, a low-pass filter [LPF], etc.) configured to transmit or receive an RF signal. As illustrated in transmitter chain 100 of FIG. 1A, a first VGA 110 receives an externally provided input reference signal ViT at baseband (BB) and provides a gain adjusted signal to multiplier\mixer 130. In conventional transmitter chains, ViT can be provided, for example, by a known baseband (BB) signal (not shown). Multiplier 130 receives an output signal from VGA 110 and an input signal from a local oscillator (LO; not shown) and provides an output signal to a second VGA 112. The output of second VGA 112 is then provided (directly or indirectly) to an nth VGA 114, which provides output signal VoT.
As illustrated, the plurality of VGAs (e.g., 110, 112, and 114) and the multiplier and\or mixer (i.e., multiplier 130) are serially coupled or connected. Generally, the transmitter chain 100 can comprise n serially coupled or connected amplification devices (e.g., VGAs 110, 112, and 114 of FIG. 1A), where n is a positive integer greater than or equal to 1. Utilizing an output signal (e.g., VoT provided by nth VGA 114 of FIG. 1A), the voltage gain (GT) of the transmitter chain 100 can be calculated according to Equation [1] below:GT=VoT/ViT  [1]where VoT is the voltage at an output 140 from an nth VGA (e.g., VGA 114 of FIG. 1A) and ViT is the known voltage of an internally and externally provided baseband (BB) reference signal (e.g., ViT of FIG. 1A). Thus, once VoT is determined, the gain GT of the transmitter 100 can be calculated.
Similarly, as illustrated in receiver chain 200 of FIG. 1B, an input RF reference signal ViR is provided to first VGA 210 at node 220 and processed by receiver chain 200 (e.g., VGAs 210, 212, and 214, and multiplier and\or mixer 230). A gain-adjusted output signal VoR is then provided by nth VGA 214 at node 240. As illustrated, the amplification devices (e.g., VGAs 210, 212, and 214) are serially coupled or connected. By utilizing an output signal (e.g., VoR provided by nth VGA 214 of FIG. 1B), a voltage gain (GR) of the receiver chain 200 can be calculated according to Equation [2] below:GR=VoR/ViR  [2]where ViR is the known voltage of an externally provided RF reference signal (e.g., ViR of FIG. 1B) at node 220, and VoR is the voltage at an output 240 provided by an nth VGA (e.g., VGA 207 of FIG. 1B) at a baseband (BB) frequency. Thus, once VoR is known, the gain GR of the receiver can be calculated.
As discussed above, to properly characterize the gain of a conventional transmitter and receiver chain (e.g., transmitter chain 100 and receiver chain 200 of FIGS. 1A and 1B, respectively), a first external device (e.g., an RF signal generator) provides an RF reference signal (ViR) for receiver gain characterization, and a second external device (e.g., a power meter, a spectrum analyzer, etc.) measures the voltage of the RF output signal of the transmitter (VoT). Gain characterization is necessary because conventional transmitters and receivers have component-dependent and temperature-dependent variations in the gain of each amplifier in the chain. For example, if a conventional CMOS amplifier has a gain of 10 dB with a possible variation of ±2 dB, the gain of the amplifier can range from 8 dB to 12 dB. Similar gain variations can also occur in other devices in the transmitter or receiver chain. Additionally, since several components (e.g., amplifiers) in a receiver or transceiver chain are cascaded together, the gain and its variation can be compounded. For example, if a receiver is designed to provide a 30 dB gain, a receiver chain comprising three 10 dB amplifiers with a ±2 dB gain variation will have a 30 dB gain with a variation of ±6 dB. Thus, the total gain from amplifier to amplifier can range from 24 dB to 36 dB. Therefore, gain characterization is required for the amplifier to achieve the target (or required) gain accuracy.
Furthermore, since the gain of such chains typically varies with respect to an input power level, the power of the input signal is typically swept to accurately determine the gain characteristics of the transmitter and receiver chains 100 and 200, respectively, at various signal input levels. Such gain measurements, however, can consume substantial amounts of time to test both the transmitter and receiver chains (a variable cost), and to setup the test procedure and environment (a fixed cost). Short test times, and reduced setup times and equipment costs, may be beneficial or critical. In addition, conventional methods of gain calibration may also be compromised by test signal imperfections (e.g., reference signal fluctuations, noise, etc.) as well as variations in the calibration equipment itself.
In receiver chains comprising VGAs (e.g., receiver chain 200 in FIG. 1B), the gain of at least one of the VGAs is programmed to obtain the desired receiver gain. For example, if a receiver chain is to provide a 30 dB gain, when the receiver chain 200 is 28 db, an amplifier in the receiver chain can be programmed or adjusted to add 2 dB of gain to it. Conventional methods of programming such VGA(s) utilize calibration during manufacturing. Specifically, a known reference signal (e.g., signal ViR in FIG. 1B) is provided (e.g., by an RF signal generator) to an input of the receiver chain 200, and the output is measured, utilizing an on-chip ADC, to obtain the gain of the receiver chain 200. The VGA(s) are then adjusted until the desired output gain is provided.
This “Background” section is provided for background information only. The statements in this “Background” are not an admission that the subject matter disclosed in this “Background” section constitutes prior art to the present disclosure, and no part of this “Background” section may be used as an admission that any part of this application, including this “Background” section, constitutes prior art to the present disclosure.